Nutrient retention after crop harvest in a typic hapludults amended with biochar types under no-tillage system

The utilization of biochar’s as soil amendments for enhancing nutrient retention in subsoils present potential limitations. To address this issue, we conducted a greenhouse experiment to assess the effects of various biochar’s derived from animal manures (swine manure, poultry litter, cattle manure) and plant residues (rice straw, soybean straw, corn straw) when applied to surface of an acidic soil. Our study focused on wheat crops under a no-tillage system, with a subsequent evaluation of the residual impacts on soybeans. The experimental design involved the application of biochar’s at different rates i.e. 10 and 20 Mg ha−1, followed by the assessment of their influence on NPK levels, pH, and exchangeable Al in stratified soil layers (0–5, 5–10, 10–15, and 15–25 cm). Furthermore, we investigated the interplay between biochar doses and the application of nitrogen (N) in the top 5 cm of soil, specifically examining \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{NO}}_{{3}}^{ - }$$\end{document}NO3-, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{NH}}_{{4}}^{ + }$$\end{document}NH4+, P and K levels. Our findings revealed that in the top 5 cm of soil, biochar doses and N application significantly affected \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{NO}}_{{3}}^{ - }$$\end{document}NO3-, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{NH}}_{{4}}^{ + }$$\end{document}NH4+, P and K concentrations. However, in deeper soil layers, no significant differences were observed among biochar doses with or without N application. Interestingly, K levels were impacted throughout all soil depths, regardless of the presence or absence of N application. Moreover, biochar application up to a 5 cm depth induced favorable changes in soil pH and reduced exchangeable Al. In contrast, deeper layers experienced a decrease in soil pH and an increase in exchangeable Al following biochar treatment. In conclusion, our study demonstrates that biochar’s can effectively retain NPK nutrients, enhance soil pH, and decrease exchangeable Al, independent of the type and dosage of application under a no-tillage system. Nonetheless, the efficacy of biochar amendments may vary with soil depth and type of nutrient, warranting careful consideration for maximizing their benefits in sustainable agricultural practices.

reduce aluminum phytotoxicity by forming surface complexes with aluminum cations 16 .As biochar application rate increased, significant increases were observed in exchangeable base cations and decreases in exchangeable acidity and Al saturation, but no additional changes in soil pH.The elimination of exchangeable acidity and the strong buffering capacity of biochar may be partially responsible for the lack of change in soil pH at the higher biochar application rate, inhibiting a further liming effect 17 .However, the outcomes of this application in such soils can exhibit variability 18,19 .The nitrification process is regulated by several factors, including soil pH, temperature, soil moisture, nitrogen (N) supplying substrate, soil microbes, and soil types.These elements play crucial roles in shaping the rate and efficiency of nitrification in the soil ecosystem 20 , as the nitrification process is major factor in N cycle in soil as well as nutrient use efficiency [21][22][23] .Understanding the nitrification process and its environmental implications for various soil types is crucial for enhancing soil fertility and promoting environmental protection.It is essential to comprehend soil processes affected by factors such as Low pH, high Al, and low CEC, which significantly limit crop growth.The common practice of using liming on acid soils to elevate pH and boost crop yields requires careful consideration 24 .Prolonged and excessive liming can lead to soil compaction, disrupt the balance of Ca, K, and Mg in the soil, ultimately resulting in reduced crop productivity 25 .A number of studies have been reporting to understand the nitrification and acidification in forests and temperate soil 26 .The attention towards the potential advantages of no-tillage has increased, particularly concerning carbon sequestration, CO 2 emissions mitigation, and improvement of soil quality 27 .The understanding of NH + 4 application effects in tropical and subtropical regions under a no-tillage system is currently limited, with scant information available [28][29][30] .Considering the significance of managing acidic soils and improving soil fertility to enhance agricultural production, we chose to utilize biochar's derived from animal manures and plant residues.
The biochars, mostly negatively charged material 31 and being high surface charge can enhance the nutrient retention and use in soil 32 having great potential for improving soil fertility 33 .Biochar application to soils can magnificently hold onto the nutrients that are required plants.However, the relationship between nutrient retention and loss pathways is still not obvious.The present study, we designed to find out the retention of nutrients C, N ( NO − 3 , NH + 4 ), P, K and micronutrients through the application of animal manures and plant residues derived biochars under greenhouse conditions.Our objective was to raise soil pH, reduce soil acidity, and boost nutrients retention in soil by using biochars derived from animal manures and plant residues.This study focused on evaluating nutrient retention in the soil after two consecutive crops of wheat and soybean, comparing plots with and without NH + 4 fertilizer application.We hypothesized that the biochar's from various animal manures and plant residues would enhance soil nutrient retention capacity and increase soil pH in different soil layers.Additionally, we expected that the biochar's would slow down the nitrification process, thereby promoting the retention of nitrogen in the NH + 4 form.

Soil collection
The soil collection site was selected on basis of no-till areas, according to the data available from the Department of Soil Science of the Federal University of Santa Maria (29° 43′ 14.2″ S 53° 42′ 15.0″ W).The vegetative cover and grasses were removed manually prior to collecting the soil.The un-disturbed soil was collected in polyvinyl pipes (PVC) (0.29 m height × 0.20 m diameter) up to 25 cm were collected for experiments under no-tillage system for pre-sowing analysis and for experimental use.Prior to installing experiments, the soil was analyzed for pH (4.8 (1:2.5 w/v)), total C (1.2%), N (0.8%), P (4.8 mg kg −1 ), K (28 mg kg −1 ), Ca (15.5 cmol c dm −3 ), Mg (9.3 cmol c dm −3 ) and Al (16.89 cmol c dm −3 ).The collected soil having sandy loam texture of the soil (61.71% sand, 25.72% silt, 12.56% clay) was classified as typic hapludults (USDA Soil Taxonomy).

Biochar preparation and analysis
To prepare the biochars, data was collected to find out the quantity and type of feedstock available and decided to collect the materials available easily and are even having any kind of difficulty in their dispose-off.For biochar's preparation, all feedstocks were collected from the experimental areas of the Federal University of Santa Maria-RS (29° 43′
As the biochars derived from plant residues had a huge volume, all the biochars were mixed up to 3 cm to have a good contact between soil and biochar to ensure seed placement in good contact with soil biochar mixture.Eight wheat seeds (Sinuelo variety) were sown into each PVC column, after germination thinning was done and four healthy seedlings were left for growth up to 93 days.After wheat harvest, three out of six soybean (5958 RSF

Statistical analysis
Standard statistical analysis was performed on collected data 34 .Analysis of variance was conducted to check the significance of treatments and to compare means of the treatment with controls and with other treatment using software R using linear model (version 3.

Ethics approval and consent to participate
We all declare that manuscript reporting studies do not involve any human participants, human data, or human tissue.So, it is not applicable.Our experiment follows the with relevant institutional, national, and international guidelines and legislation.

Primary nutrients concentration
It has been recognized that biochars can adsorb both NO − 3 and NH + 4 nitrogen because of their large surface areas and presence of a range of different functional groups, consequently increasing the soil fertility and crop production.On biochar's surface both acidic and basic sites can be found which can affect the adsorption of cations as well anions 35 .From the results (Table 1) in layer 0-5 cm, it can be seen that retention of NO form.The N application to soil decreased the NO − 3 in columns with CMB, SSB and CSB both in 10 as well as 20 Mg ha −1 .Data on soil layer 5-10 cm (Table 2) shows that increase in depth of soil decreased the NO − 3 retention in soil both in different biochar types as well as doses of biochar's.There was no effect was noted among different biochar types, even with different doses of biochar's i.e., 10 and 20 Mg ha −1 .The N application to crops also didn't affect the NO − 3 in soil after harvest.Maximum NO − 3 (8.0mg kg −1 ) was observed in soil column amended with SMB at 20 Mg ha −1 while Minimum (1.1 mg kg −1 ) was observed in soil column treated with SSB at 20 Mg ha −1 .No NO − 3 was found in deeper layers i.e., 10-15 and 15-10 cm (Tables 3 and 4) even an application of N fertilizer to an acidic soil had no effect on soil NO − 3 contents under no tillage conditions.Presence of NO − 3 in soil layer 0-5 cm confirms the nitrification process occurs in topsoil which was mixed with biochar (2.5-3 cm) based on the great volumes of the plant residues derived biochars.The application of alkaline biochar with high adsorptive capability adsorbs NO − 3 and NH + 4 and hence reduce N loss from soil 36 .Biochars being porous and high exchange nature material can adsorb more nutrients, enhancing the soil nitrogen contents 37,38 .A high amount of nitrogen is attached by biochars when they are applied in high rates in soil 39 .The NH + 4 contents in soil were not affected by different biochar types after crop harvest (Table 1), even increase in dose of biochar's had no significant effect in NH + 4 retention in soil in topsoil layer (0-5 cm).A slight increase in NH + 4 was observed with increase in dose of each biochar.Ammonium content in soil was also influenced directly with application of NH + 4 fertilizer in soil in wheat crop under no tillage system.The N application increased the NH + 4 retention in soil while the dose of biochar had not a significant effect on NH + 4 retention in top 5 cm soil layer.Maximum NH + 4 (67.6 mg kg −1 ) was observed with application of CSB at 20 Mg ha −1 whereas minimum was observed in control treatment (control with N application).The most important biochar physical property to retain NH + 4 and NH 3 is the surface   40 .However, NH 3 being an alkaline gas, the acidic surface groups on biochar with low pH can protonate NH 3 gas to NH + 4 ions thereby promoting their adsorption onto the cation exchange sites of biochar 41 hence reducing the NH + 4 loss through NH 3 .In soil layer 5-10 cm decreased NH + 4 content as compared to top 5 cm soil, the decrease in NH + 4 concentration shows the weak influence of surface application of biochar's derived from animal manures and plant residues.Resaee et al. 42 noted that biochars with higher O/C ratio can have more NH + 4 adsorption as compared to biochars with less O/C, likewise Wang et al. 43 found a direct relationship between functional groups and NH + 4 adsorption.An increase can be seen with increase in dose of biochar's but there was not statistically (p < 0.05) significant difference found between the two doses of biochars.The application of N to soil also didn't affect the NH + 4 in soil up to 10 cm depth.A decrease and slight increase can be observed in both doses of biochar's for example, in soil column SMB had NH + 4 contents 15.7 mg kg −1 at 10 Mg ha −1 that decreased with 20 Mg ha −1 to 6.6 mg kg −1 while in case of CSB increased from 9.3 mg kg −1 to12.2 mg kg −1 with increase in dose of biochar.In both control treatments (with N and without N) NH + 4 was almost same 15.5 mg kg −1 without N and 14.6 m kg −1 with N application.As compared to NO − 3 , the NH + 4 was found continuously up to 25 cm layers collections (Tables 3 and 4), but with the increase in soil depth the concentration also remained gradually decreasing.There are number of studies showing that the addition of biochars lower the loss of NO − 3 through leaching and increase its concentrations in soil were for short period of time while long term experiments were still overlooked.According to Coa et al. 44 , the inclusion of biochar improved NO − 3 retention in the early phases of the experiment, while NO − 3 N loss by leaching increased in the later stages.Kameyama et al. 45 reported adsorption of NO − 3 primarily caused by base functional groups rather than physical sorption thus biochar and NO 3 − adsorption relationship is weak.On the other hand, the NO − 3 adsorption may  www.nature.com/scientificreports/be attributed to electrostatic interactions and ion exchange phenomena 46 .The increase in dose of biochar's had also a little influence in NH + 4 contents whereas there was not a significant between doses of biochar's, even in case of SSB and CSB the NH + 4 content decreased 78 and 38% respectively with increase in dose of biochar (Table 3).With increase in soil depth the NO − 3 contents decreased and in final 2 layers (10-15 and 15-25 cm) no NO − 3 was noted that can be directly attributed to the no tillage soil conditions that we couldn't mix the soil and biochar at grater depths.The available P remained changing with increase in depth, in top 0-5 cm layer P was influenced with biochar types as well as the increase in dose of biochar's under no tillage system.Highest P (177.9 mg kg −1 ) was found in soil column treated with CMB at 10 Mg ha −1 while minimum (33.7 mg kg −1 ) was observed in control (no biochar, no N).The addition of N fertilizer enhanced the P retention in soil in all treatments with 20 Mg ha −1 except the soil treated with SMB where the addition of N fertilizer decreased the P content in soil i.e., 247 mg kg −1 without N and 206.6 mg kg −1 with the addition of N, while the P contents remained non-significant with biochar's dose at 10 Mg ha −1 with N application together.In control treatments addition of N also increased the P retention in soil.With increase in depth, decrease in available P (Table 2) was observed but among different biochar types, no difference was observed when applied at 10 and 20 Mg ha −1 without N fertilizer while a huge increase was noted in column treated with SMB at 20 Mg ha −1 as compared to 10 Mg ha −1 .The addition of N fertilizer also had not a significant impact on available P contents between 5 and 10 cm depth.In control treatments, no difference was found with and without application of mineral N fertilizer.As compared to topsoil layers 0-5 and 5-10 cm, the available P in the subsoil layers (10-15 and 15-25 cm) was remained uninfluenced with different biochar types, doses of biochar's as well as in combination with mineral N fertilizer (Tables 3 and 4), while a minute different among treatments and doses can be noted.In the acidic soils, the P sorption is higher than the neutral or alkaline soil because of its low pH and Fe, Al and Mn oxides are dominant at low pH and fix P and reduce its availability 47 .Addition of biochar's in low pH soil can decrease the soil pH and increase available P in soil solution by the increase in negative charged surfaces and pH may be increased by proton consumption reaction and hence forming hydro-oxides of Al and Fe.The biochar types, doses of biochar's as well as combination of N strongly affected the available K in soil after the crop harvest.The available K ranged from 15 to 248 mg kg −1 affected by control (no biochar, no N) and RSB respectively without an application of N fertilizer (Table 1).The application of N decreased the k retention significantly in both 10 and 20 Mg ha −1 .With increase in soil depth the available K concentration decreased while the influence of different biochar's on K remained significant among different biochar types, doses, and combination of N. in sublayer 5-10 cm highest K (267.7 mg kg −1 ) was observed in soil column treated with RSM at 20 Mg ha −1 while minimum (14.3 mg kg −1 ) was observed in control treatment (no biochar, no N) (Table 2).From the data (Tables 3 and 4) similar behavior has been observed that with increase in biochar dose the K content increases while the addition of mineral N fertilizer decreases the K contents in soil.

Soil pH and Al alteration
Biochar pH ranges from 5.5 to 10.5, that depends on content and composition of the mineral fractions that may be different depending upon the feedstock and pyrolysis [48][49][50][51][52] That's why biochar can alter the NH + 4 and NO − 3 dynamic in soil system through their adsorptive properties and pH.Soil pH was greatly influenced by the addition of biochar's alone, and along with NH + 4 fertilizer (Fig. 1A, B, C and D).The addition of biochar's at 10 Mg ha −1 increased the soil pH sufficiently, highest soil pH was observed from the soil column treated with CSB, SSB, PLB and RSB as well in layer 0-5 cm.With increase in soil depth pH also decreased gradually even CSB, SSB and PLB decreased in layer 5-10 cm and remained decreased up to 15-25 cm (Fig. 1A).Increased dose of biochar's also increased the soil pH drastically.Soil treated with RSB at 20 Mg ha −1 showed maximum soil pH, whereas SSB didn't increase the soil pH with an increase in its dose (Fig. 1B).On the other hand, RSB decreased the soil pH in sublayer (15-25 cm) again up to an acidic level.Application of ammonium fertilizer also had an influence on soil pH in layer 0-5 cm, because in addition to NH 4 fertilizer pH was increased up to a certain level (PLB, SMB), after that level then decreased quickly in 5-10 cm layer at 10 Mg ha −1 while PLB remained in slow decrease as compared to SMB at 20 Mg ha −1 .In deeper soil layers there are not significant differences can be noted but the pH remained decreasing with increase in soil depth.The pH increase in surface layer can be related to the presence of biochar's negatively charged phenolic, carboxyl and hydroxyl groups on surface of biochar which tend to bind H + from soil solution by reducing soil H + and hence increase in pH 53,54 .The pH increment increases the CEC by reducing the base cations leaching in competition H + ions 55 .In our studies the biochar affected the only surface layer while underneath layers were not affected directly with addition of biochar even at 20 Mg ha −1 .The addition of NH + 4 as fertilizer in soil decreases the soil pH whereas an increase occurs with application of biochar to an acid soil 56 A huge gradient can be seen by addition of different biochar's in soil under undisturbed soil (no tillage system).Minimum exchangeable Al was observed in soil layer 0-5 cm (Fig. 2A, B,  C, D), that kept it increasing with increase in soil depth.Lowest exchangeable Al was observed in SSB at both 10 and 20 Mg ha −1 .The addition of ammonium fertilizer didn't influence the exchangeable Al content in an acidic soil under no tillage system while the influence of amendment was limited to a very shallow depth (5 cm), after that remained increasing and reached near to its original Al content in both 10 and 20 Mg ha −1 .The addition of biochar's increases the alkaline metals (Ca 2+ , Mg 2+ and K + ) oxides in acidic soil and hence soluble Al 3+ reduces by an increase in pH 3,[57][58][59][60][61] .

Conclusion
Surface application of different biochar can have a limited impact on soil nutrients especially to an acidic soil.The biochar's had a significant effect up to 5 cm soil depth by retaining NO − 3 while can hold higher quantities of NH + 4 up to more depths under no tillage system.Phosphorus can be adsorbed by biochar's when applied at surface while in deeper layers biochar's don't influence the P retention in soil.Potassium is greatly influenced with